Spatial distribution and seasonal variation of atmospheric bulk deposition of polycyclic aromatic hydrocarbons in Beijing-Tianjin region, North China

Bulk deposition samples were collected in remote, rural village and urban areas of Beijing-Tianjin region, North China in spring, summer, fall and winter from 2007 to 2008. The annually averaged PAHs concentration and deposition flux were 11.81 ± 4.61 μg/g and 5.2 ± 3.89 μg/m²/day respectively. PHE and FLA had the highest deposition flux, accounting for 35.3% and 20.7% of total deposition flux, respectively. More exposure risk from deposition existed in the fall for the local inhabitants. In addition, the PAHs deposition flux in rural villages (3.91 μg/m²/day) and urban areas (8.28 μg/m²/day) was 3.8 and 9.1 times higher than in background area (0.82 μg/m²/day), respectively. This spatial variation of deposition fluxes of PAHs was related to the PAHs emission sources, local population density and air concentration of PAHs, and the PAHs emission sources alone can explain 36%, 49%, 21% and 30% of the spatial variation in spring, summer, fall and winter, respectively.     

Atmospheric partitioning and the air–water exchange of polycyclic aromatic hydrocarbons in a large shallow Chinese lake (Lake Chaohu)

The residual levels of polycyclic aromatic hydrocarbons (PAHs) in the atmosphere and in dissolved phase from Lake Chaohu were measured by (GC–MS). The composition and seasonal variation were investigated. The diffusive air–water exchange flux was estimated by a two-film model, and the uncertainty in the flux calculations and the sensitivity of the parameters were evaluated. The following results were obtained: (1) the average residual levels of all PAHs (PAH16) in the atmosphere from Lake Chaohu were 60.85 ± 46.17 ng m⁻³ in the gaseous phase and 14.32 ± 23.82 ng m⁻³ in the particulate phase. The dissolved PAH16 level was 173.46 ± 132.89 ng L⁻¹. (2) The seasonal variation of average PAH16 contents ranged from 43.09 ± 33.20 ng m⁻³ (summer) to 137.47 ± 41.69 ng m⁻³ (winter) in gaseous phase, from 6.62 ± 2.72 ng m⁻³ (summer) to 56.13 ± 22.99 ng m⁻³ (winter) in particulate phase, and 142.68 ± 74.68 ng L⁻¹ (winter) to 360.00 ± 176.60 ng L⁻¹ (summer) in water samples. Obvious seasonal trends of PAH16 concentrations were found in the atmosphere and water. The values of PAH16 for both the atmosphere and the water were significantly correlated with temperature. (3) The monthly diffusive air–water exchange flux of total PAH16 ranged from −1.77 × 10⁴ ng m⁻² d⁻¹ to 1.11 × 10⁵ ng m⁻² d⁻¹, with an average value of 3.45 × 10⁴ ng m⁻² d⁻¹. (4) The results of a Monte Carlo simulation showed that the monthly average PAH fluxes ranged from −3.4 × 10³ ng m⁻² d⁻¹ to 1.6 × 10⁴ ng m⁻² d⁻¹ throughout the year, and the uncertainties for individual PAHs were compared. (5) According to the sensitivity analysis, the concentrations of dissolved and gaseous phase PAHs were the two most important factors affecting the results of the flux calculations.     

Total gaseous concentrations in mercury in Seoul, Korea: Local sources compared to long-range transport from China and Japan

Total gaseous mercury (TGM) and carbon monoxide (CO) were measured every 5 min and hourly, respectively, in Seoul, Korea, from February 2005 through December 2006. The mean concentrations of TGM and CO were 3.44 ± 2.13 ng m⁻³ and 613 ± 323 ppbv, respectively. TGM and CO concentrations were highest during the winter and lowest during the summer. In total, 154 high TGM concentration events were identified: 86 were classified as long-range transport events and 68 were classified as local events. The TGM and CO concentrations were well correlated during all long-range transport events and were weakly correlated during local events. Five-day backward trajectory analysis for long-range transport events showed four potential source regions: China (79%), Japan (13%), the Yellow Sea (6%), and Russia (2%). Our results suggest that measured ΔTGM/ΔCO can be used to identify long-range transported mercury and to estimate mercury emissions from long-range transport.     

Temporal patterns of atmospheric mercury species in northern Mississippi during 2011–2012: Influence of sudden population swings

Gaseous elemental mercury (GEM), gaseous oxidized mercury (GOM) and particulate bound mercury (PBM) were measured on the University of Mississippi campus from July 2011 to June 2012. It is believed to be the first time that concentrations of atmospheric mercury species have been documented in northern Mississippi, and at a location with relatively large and sudden swings in population. The mean concentration (±1SD) of GEM was 1.54 ± 0.32 ng m⁻³; levels were lower and generally more stable during the winter (1.48 ± 0.22) and spring (1.46 ± 0.27) compared with the summer (1.56 ± 0.32) and fall (1.63 ± 0.42). Mean concentrations for GOM and PBM were 3.87 pg m⁻³ and 4.58 pg m⁻³, respectively; levels tended to be highest in the afternoon and lowest in the early morning hours. During the fall and spring academic semesters concentrations and variability of GOM and PBM both increased, possibly from vehicle exhaust. There were moderate negative correlations with wind speed (all species) and humidity (GOM and PBM). Backward air mass trajectory modeling for the ten highest peaks for each mercury species revealed that the majority of these events occurred from air masses that passed through the northern continental US region. Overall, this study illustrates the complexity of temporal fluctuations of airborne mercury species, even in a small town environment.     

Vapor-phase concentrations of PAHs and their derivatives determined in a large city: Correlations with their atmospheric aerosol concentrations

Thirteen PAHs, five nitro-PAHs and two hydroxy-PAHs were determined in 55 vapor-phase samples collected in a suburban area of a large city (Madrid, Spain), from January 2008 to February 2009. The data obtained revealed correlations between the concentrations of these compounds and a series of meteorological factors (e.g., temperature, atmospheric pressure) and physical–chemical factors (e.g., nitrogen and sulfur oxides). As a consequence, seasonal trends were observed in the atmospheric pollutants. A “mean sample” for the 14-month period would contain a total PAH concentration of 13 835 ± 1625 pg m⁻³ and 122 ± 17 pg m⁻³ of nitro-PAHs. When the data were stratified by season, it emerged that a representative sample of the coldest months would contain 18 900 ± 2140 pg m⁻³ of PAHs and 150 ± 97 pg m⁻³ of nitro-PAHs, while in an average sample collected in the warmest months, these values drop to 9293 ± 1178 pg m⁻³ for the PAHs and to 97 ± 13 pg m⁻³ for the nitro-PAHs. Total vapor phase concentrations of PAHs were one order of magnitude higher than concentrations detected in atmospheric aerosol samples collected on the same dates. Total nitro-PAH concentrations were comparable to their aerosol concentrations whereas vapor phase OH-PAHs were below their limits of the detection, indicating these were trapped in airborne particles.     

Dry deposition and soil-air gas exchange of polychlorinated biphenyls (PCBs) in an industrial area

Ambient air and dry deposition, and soil samples were collected at the Aliaga industrial site in Izmir, Turkey. Atmospheric total (particle + gas) ∑₄₁-PCB concentrations were higher in summer (3370 ± 1617 pg m⁻³, average + SD) than in winter (1164 ± 618 pg m⁻³), probably due to increased volatilization with temperature. Average particulate ∑₄₁-PCBs dry deposition fluxes were 349 ± 183 and 469 ± 328 ng m⁻² day⁻¹ in summer and winter, respectively. Overall average particulate deposition velocity was 5.5 ± 3.5 cm s⁻¹. The spatial distribution of ∑₄₁-PCB soil concentrations (n = 48) showed that the iron-steel plants, ship dismantling facilities, refinery and petrochemicals complex are the major sources in the area. Calculated air-soil exchange fluxes indicated that the contaminated soil is a secondary source to the atmosphere for lighter PCBs and as a sink for heavier ones. Comparable magnitude of gas exchange and dry particle deposition fluxes indicated that both mechanisms are equally important for PCB movement between air and soil in Aliaga.     

Atmospheric mercury pollution at an urban site in central Taiwan: mercury emission sources at ground level

Total gaseous mercury (Hg) (TGM), gaseous oxidized Hg (GOM), and particulate-bound Hg (PBM) concentrations and dry depositions were measured at an urban site in central Taiwan. The concentrations were 6.14 ± 3.91 ng m⁻³, 332 ± 153, and 71.1 ± 46.1 pg m⁻³, respectively. These results demonstrate high Hg pollution at the ground level in Taiwan. A back trajectory plot shows the sources of the high TGM concentration were in the low atmosphere (<500 m) and approximately 50% of the air masses coming from upper troposphere (>500 m) were associated with low TGM concentrations. This finding implies that Hg is trapped in the low atmosphere and comes from local Hg emission sources. The conditional probability function (CPF) reveals that the plumes of high TGM concentrations come from the south and northwest of the site. The plume from the south comes from two municipal solid waste incinerators (MSWIs). However, no significant Hg point source is located to the northwest of the site; therefore, the plumes from the northwest are hypothesized to be related to the combustion of agricultural waste. Dry deposition fluxes of Hg measured at this site considerably exceeded those measured in North America. Overall, this area is regarded as a highly Hg contaminated area because of local Hg emission sources.     

Atmospheric concentrations,gaseous–particulate distribution,and carcinogenic potential of polycyclic aromatic hydrocarbons in Assiut,Egypt

The concentrations of 15 priority PAHs were determined in the atmospheric gaseous and particulate phases from nine sites across Assiut City, Egypt. While naphthalene, acenaphthene, and fluorene were the most abundant in the gaseous phase with average concentrations of 377, 184, and 181 ng/m³, benzo[b]fluoranthene, chrysene, and benzo[g,h,i]perylene showed the highest levels in the particulate phase with average concentrations of 76, 6, and 52 ng/m³. The average total atmospheric concentration of target PAHs (1,590 ng/m³) indicates that Assiut is one of the highest PAH-contaminated areas in the world. Statistical analysis revealed a significant difference between the levels of PAHs in the atmosphere of urban and suburban sites (P?=?0.029 and 0.043 for gaseous and particulate phases, respectively). Investigation of diagnostic PAH concentration ratios revealed vehicular combustion and traffic exhaust emissions as the major sources of PAHs with a higher contribution of gasoline rather than diesel vehicles in the sampled areas. Benzo[a]pyrene has the highest contribution (average?=?32, 4 % for gaseous and particulate phases) to the total carcinogenic activity (TCA) of atmospheric PAHs. While particulate phase PAHs have higher contribution to the TCA, gaseous phase PAHs present at higher concentrations in the atmosphere are more capable of undergoing atmospheric reactions to form more toxic derivatives.     

Polycyclic aromatic hydrocarbons in indoor and outdoor air in Turkey: Estimations of sources and exposure

The aim of the current study was to measure polycyclic aromatic hydrocarbons (PAHs) in eight indoor (In both kitchen and living room) air sampling locations using a passive sampling method for collection. Passive outdoor air samples were also collected from 3 of the same sampling locations as the indoor air sampling sites. Sampling was conducted in three seasons. The summer season, when windows are generally open, was between 18th July and 01st September, 2014; the autumn and winter seasons, when windows are mostly closed, was between 18^th October and 01^st December, 2014, and 01^st December, 2014, and 18^th January, 2015, respectively.

Average PAH concentrations in summer were 22 ± 21 ng/m³ and 17 ± 12 ng/m³ in the living room and kitchen, respectively, whereas living room and kitchen average PAH concentrations were 23 ± 16 ng/m³ and 20 ± 9 ng/m³, respectively, in autumn and 23 ± 13 ng/m³ and 23 ± 24 ng/m³, respectively, in winter. Outdoor air PAH concentrations in summer, autumn and winter were 7 ± 0.4 ng/m³, 22 ± 13 ng/m³ and 209 ± 33 ng/m³, respectively. An increase in outdoor PAH concentrations was measured in winter compared to the concentrations in summer and autumn, which paralleled the lower outdoor air temperature. However, PAH concentrations in the indoor environment vary according to the household characteristics and personal habits.     

Impact of anthropogenic emissions and open biomass burning on regional carbonaceous aerosols in South China

Carbonaceous aerosols were studied at three background sites in south and southwest China. Hok Tsui in Hong Kong had the highest concentrations of carbonaceous aerosols (OC = 8.7 ± 4.5 μg/m³, EC = 2.5 ± 1.9 μg/m³) among the three sites, and Jianfeng Mountains in Hainan Island (OC = 5.8 ± 2.6 μg/m³, EC = 0.8 ± 0.4 μg/m³) and Tengchong mountain over the east edge of the Tibetan Plateau (OC = 4.8 ± 4.0 μg/m³, EC = 0.5 ± 0.4 μg/m³) showed similar concentration levels. Distinct seasonal patterns with higher concentrations during the winter, and lower concentrations during the summertime were observed, which may be caused by the changes of the regional emissions, and monsoon effects. The industrial and vehicular emissions in East, Southeast and South China, and the regional open biomass burning in the Indo-Myanmar region of Asia were probably the two major potential sources for carbonaceous matters in this region.     

The sea–air exchange of mercury (Hg) in the marine boundary layer of the Augusta basin (southern Italy): Concentrations and evasion flux

The first attempt to systematically investigate the atmospheric mercury (Hg) in the MBL of the Augusta basin (SE Sicily, Italy) has been undertaken. In the past the basin was the receptor for Hg from an intense industrial activity which contaminated the bottom sediments of the Bay, making this area a potential source of pollution for the surrounding Mediterranean. Three oceanographic cruises have been thus performed in the basin during the winter and summer 2011/2012, where we estimated averaged Hg_atm concentrations of about 1.5 ± 0.4 (range 0.9–3.1) and 2.1 ± 0.98 (range 1.1–3.1) ng m⁻³ for the two seasons, respectively. These data are somewhat higher than the background Hg_atm value measured over the land (range 1.1 ± 0.3 ng m⁻³) at downtown Augusta, while are similar to those detected in other polluted regions elsewhere. Hg evasion fluxes estimated at the sea/air interface over the Bay range from 3.6 ± 0.3 (unpolluted site) to 72 ± 0.1 (polluted site of the basin) ng m⁻² h⁻¹. By extending these measurements to the entire area of the Augusta basin (∼23.5 km²), we calculated a total sea–air Hg evasion flux of about 9.7 ± 0.1 g d⁻¹ (∼0.004 t yr⁻¹), accounting for ∼0.0002% of the global Hg oceanic evasion (2000 t yr⁻¹). The new proposed data set offers a unique and original study on the potential outflow of Hg from the sea–air interface at the basin, and it represents an important step for a better comprehension of the processes occurring in the marine biogeochemical cycle of this element.     

Levels and speciation of arsenic in the atmosphere in Beijing, China

Arsenic levels and speciation in the total suspended particles (TSPs) were quantitatively determined by high performance liquid chromatography on-line coupled with hydride generation atomic fluorescence spectrometry in Beijing, China from February 2009 to March 2011. The high TSP levels fluctuated between 0.07 and 0.79 mg m⁻³, with a mean level of 0.32 ± 0.17 mg m⁻³. The total arsenic concentrations ranged from 0.03 to 0.31 μg m⁻³ (mean: 0.13 ± 0.06 μg m⁻³) in Beijing‘s air. The concentrations of As(III) and As(V) ranged from 0.73 to 20 ng m⁻³ (mean: 4.7 ± 3.6 ng m⁻³) and from 14 to 2.5 × 10² ng m⁻³ (mean: 67 ± 35 ng m⁻³), respectively. As levels and speciation demonstrated relative higher levels in spring and autumn and lower values in summer and winter. As(V) accounted for 81-99% of the extractable species in the TSP samples which showed that As(V) was the major fraction of the extractable As. Organoarsenic species, monomethylarsonate (MMA) and dimethylarsinate (DMA) were not found in all samples. Higher values of enrichment factors demonstrated that arsenic in TSP mainly come from anthropogenic sources. High As and its species levels in air and respiratory exposure (0.30-0.84 μg d⁻¹) attributed to higher excess cancer risk ((4.2 ± 2.0) × 10⁻⁴) for people in Beijing.     

Wastewater treatment plants and landfills emit volatile methyl siloxanes (VMSs) to the atmosphere: investigations using a new passive air sampler

Volatile methyl siloxanes (VMSs) are a class of chemicals with an increasing range of applications and widespread distribution in the environment. Passive air samplers (PAS) comprising sorbent-impregnated polyurethane-foam (SIP) disks were first calibrated and then deployed around two wastewater treatment plants (WWTPs) and at two landfill sites to investigate inputs of VMSs to air. SIP-derived air concentrations for ΣVMSs (ng/m³) at background sites on the perimeter of the WWTP were 479 ± 82.3 and comparable to results for the upwind samples at the landfills (333 ± 194). Order of magnitude higher concentrations of ΣVMSs (ng/m³) were found for on-site samples at the WWTPs (3980 ± 2620) and landfills (4670 ± 3360). Yearly emissions (kg/yr) to air were estimated and ranged from 60-2100 and 80-250, respectively, for the cyclic VMSs. These findings demonstrate and quantify for the first time, waste sector emissions of VMSs to the atmosphere.     

Evaluation of atmospheric sources of PCDD/Fs, PCBs and PBDEs around a steel industrial complex in northeast China using passive air samplers

The concern about emissions of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) polychlorinated biphenyls (PCBs), and polybrominated diphenyl ethers (PBDEs) from steel industrial parks has increased in the past decades. In this study, polyurethane foam (PUF)-disk based passive air samples were collected in and around a big steel industrial park of Anshan, Northeast China from June 2008 to March 2009. The levels, seasonal variations and potential sources of PCDD/Fs, PCBs and PBDEs in the atmosphere around the steel industrial complex were investigated, and potential contribution of these three groups of persistent organic pollutants (POPs) from iron and steel production was also assessed. The air concentrations of ∑₁₇PCDD/Fs (summer: 0.02-2.77 pg m⁻³; winter: 0.20-9.79 pg m⁻³), ∑₁₉PCBs (summer: 23.5-155.8 pg m⁻³; winter: 14.6-81.3 pg m⁻³) and ∑₁₃PBDEs (summer: 2.91-10.7 pg m⁻³; winter: 1.10-3.89 pg m⁻³) in this targeted industrial park were relatively low in comparison to other studies, which implied that the industrial activities of iron and steel had not resulted in serious contamination to the ambient air in this area. On the whole, the air concentrations of PCDD/Fs in winter were higher than those of summer, whereas the concentrations of PCBs and PBDEs showed opposite trends. The result from principal component analysis indicated that coal combustion might be the main contributor of PCDD/F sources in this area.     

Vertical distribution of polycyclic aromatic hydrocarbons in atmospheric boundary layer of Beijing in winter

Air samples were collected using active samplers at various heights of 8, 15, 32, 47, 65, 80, 102, 120, 140, 160, 180, 200, 240, 280 and 320 m on a meteorological tower in an urban area of Beijing in two campaigns in winter 2006. Altitudinal distributions of polycyclic aromatic hydrocarbons (PAHs) in atmospheric boundary layer of Beijing in winter season were investigated. Meteorological conditions during the studied period were characterized by online measurements of four meteorological parameters as well as trajectory calculation. The mean total concentrations of 15 PAHs except naphthalene of gaseous and particulate phase were 667±450 and 331±144 ng m⁻³ in January and 61±19 and 29±6 ng m⁻³ in March, respectively. Domestic coal combustion and vehicle emission were the dominant PAH sources in winter. Although the composition profiles derived from the two campaigns were similar, the concentrations were different by one order of magnitude. The higher concentrations in January were partly caused by higher emission due to colder weather than March. Moreover, weak wind, passing through the city center before the sampling site, picked up more contaminants on the way and provided unfavorable dispersion condition in January. For both campaigns, PAH concentrations decreased with heights because of ground-level emission and unfavorable dispersion conditions in winter. The concentration ratio of PAHs in gas versus solid phases was temperature dependent and negatively correlated to their octanol–air partition coefficients.     

Seasonal variation and spatial distribution of atmospheric mercury and its gas-particulate partition in the vicinity of a semiconductor manufacturing complex

This study investigated the tempospatial variation of atmospheric mercury and its gas-particulate partition in the vicinity of a semiconductor manufacturing complex, where a plenty of flat-monitor manufacturing plants using elemental mercury as a light-initiating medium to produce backlight fluorescence tubes and may fugitively emit mercury-containing air pollutants to the atmosphere. Atmospheric mercury speciation, concentration, and the partition of total gaseous mercury (TGM) and particulate mercury (Hg_p) were measured at four sites surrounding the semiconductor manufacturing intensive district/complex. One-year field measurement showed that the seasonal averaged concentrations of TGM and Hg_p were in the range of 3.30–6.89 and 0.06–0.14 ng/m³, respectively, whereas the highest 24-h TGM and Hg_p concentrations were 10.33 and 0.26 ng/m³, respectively. Atmospheric mercury apportioned as 92.59–99.01 % TGM and 0.99–7.41 % Hg_p. As a whole, the highest and lowest concentrations of TGM were observed in the winter and summer sampling periods, respectively, whereas the concentration of Hg_p did not vary much seasonally. The highest TGM concentrations were always observed at the downwind sites, indicating that the semiconductor manufacturing complex was a hot spot of mercury emission source, which caused severe atmospheric mercury contamination over the investigation region.     

Atmospheric mercury concentrations and speciation measured from 2004 to 2007 in Reno, Nevada, USA

Atmospheric elemental, reactive and particulate mercury (Hg) concentrations were measured north of downtown Reno, Nevada, USA from November 2004 to November 2007. Three-year mean and median concentrations for gaseous elemental Hg (Hg⁰) were 1.6 and 1.5 ng m⁻³ (respectively), similar to global mean Hg⁰ concentrations. The three-year mean reactive gaseous Hg (RGM) concentration (26 pg m⁻³) was higher than values reported for rural sites across the western United States. Well defined seasonal and daily patterns in Hg⁰ and RGM concentrations were observed, with the highest Hg⁰ concentrations measured in winter and early morning, and RGM concentrations being greatest in the summer and mid-afternoon. Elevated Hg⁰ concentrations in winter were associated with periods of cold, stagnant air; while a regularly observed early morning increase in concentration was due to local source and surface emissions. The observed afternoon increase and high summer values of RGM can be explained by in situ oxidation of gaseous Hg⁰ or mixing of RGM derived from the free troposphere to the surface. Because both of these processes are correlated with the same environmental conditions it is difficult to assess their overall contribution to the observed trends.     

Sources of PCDD/Fs, non-ortho PCBs and PAHs in sediments of high and low impacted transboundary rivers (Belgium-France)

PAHs, PCDD/Fs and non-ortho PCBs have been assessed in Yser and Upper-Scheldt river sediments. Higher contamination levels were observed in the Upper-Scheldt sediments: maximum concentrations for the 16 US-EPA PAHs, PCDD/Fs and non-ortho PCBs respectively amount to 8.9 mg kg⁻¹, 12 ng TEQ kg⁻¹ and 5.1 ng TEQ kg⁻¹. Diagnostic PAH ratios in sediments and atmospheric samples suggest that the PAH compounds are from pyrolytic origin, more specifically combustion processes. The huge consumption of coal in cokes-ovens and smelters and its use for house-heating in Northern France, although decreasing during the last decades, are in support of that suggestion. PCDD/F fingerprints in sediments and deposition material indicate that OCDD is the dominant congener. In addition use of pentachlorophenol (PCP) in the past led to a minor contribution of PCDD/Fs in our sediment samples. Non-ortho PCBs form a substantial fraction of the total TEQ concentrations observed in the sediments. Since the 1980s and 1990s a substantial reduction of the PCDD/F sediment concentrations is observed, but this is not the case for the PAHs.     

Phosphine in paddy fields and the effects of environmental factors

Ambient levels of phosphine (PH₃) in the air, phosphine emission fluxes from paddy fields and rice plants, and the distribution of matrix-bound phosphine (MBP) in paddy soils were investigated throughout the growing stages of rice. The relationships between MBP and environmental factors were analyzed to identify the principal factors determining the distribution of MBP. The phosphine ambient levels ranged from 2.368 ± 0.6060 ng m⁻³ to 24.83 ± 6.529 ng m⁻³ and averaged 14.25 ± 4.547 ng m⁻³. The highest phosphine emission flux was 22.54 ± 3.897 ng (m² h)⁻¹, the lowest flux was 7.64 ± 4.83 ng (m² h)⁻¹, and the average flux was 14.17 ± 4.977 ng (m² h)⁻¹. Rice plants transport a significant portion of the phosphine emitted from the paddy fields. The highest contribution rate of rice plants to the phosphine emission fluxes reached 73.73% and the average contribution was 43.00%. The average MBP content of 111.6 ng kg⁻¹fluctuated significantly in different stages of rice growth and initially increased then decreased with increasing depth. The peak MBP content in each growth stage occurred approximately 10 cm under the surface of paddy soils. Pearson correlation analyses and stepwise multiple regression analysis showed that soil temperature (Ts), acid phosphatase (ACP) and total phosphorus (TP) were the principal environmental factors, with correlative rankings of Ts > ACP > TP.